In general, a hydraulic excavator which is a typical example of a construction machine is composed of an automotive lower traveling structure, an upper revolving structure rotatably mounted on the lower traveling structure, and a working mechanism provided capable of moving upward/downward on the front side of the upper revolving structure.
The upper revolving structure is composed of a revolving frame forming a support structural body, a floor member provided on the revolving frame, in which the rear side is a seat base on which an operator's seat is mounted and the front side is a footrest area on which the operator places the foot, a cab box provided by covering the periphery and the upper part of the floor member in order to form a occupying space on the floor member, and an indoor unit of an air conditioning unit mounted on the floor member and supplying sucked air into the occupying space as conditioned air.
As the floor member according to a conventional art, the footrest area having a double-floor structure of a lower floor plate and an upper floor plate and configured such that a recess portion is formed in the lower floor plate, and the indoor unit of the air conditioning unit is accommodated in this recess portion is known. In this case, an indoor air suction port for sucking the air in the occupying space (indoor air) and an indoor air filter are arranged on the lower side of the footrest area integrally with the indoor unit (See Patent Document 1, for example).
As another conventional art, a configuration in which the indoor unit of the air conditioning unit is provided on the footrest area and located in the lower side of the operator's seat is known. In this another conventional art, the indoor air suction port is provided so as to be opened on the side of the indoor unit, and the indoor air filter is arranged at a position covering this indoor air suction port (Patent Document 2).